I have a very important question regarding the mesh study (grid independency study)

My simulation is based on mesh A in which the element size (done in ICEM) is 0.15 and the total number of elements is 1 934 000 mesh,
For grid study I decreased the size of element for two times (mesh B and C), every time it became smaller with the ratio of 15%,
So, for mesh B, the size of element is 0.1275 and the number of element is 3 048 000 mesh and
for mesh C, the size of element is 0.108375 and the number of element is 5 000 000 mesh,
then I investigated the critical parameter in the critical zone, (the difference between mesh C and A was 4%)

- My question is, whether my Grid study (independency) procedure is correct or not?
- I got a bit confused about the amount increase in elements or decrease in element size regarding to grid study as every source tell something different… is reducing the size every time by 15% OK?